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> Ah, yes. The main problems with the hierarchical model are
> that it encourages data redundancy which leads to problems
> during updates and deletions.
3rd normal form was about showing that you could move to a relational
representation of data without introducing redundancy. The problems with
hierarchical and network database systems were quite different: the lack
of declarative data manipulation languages with good closure properties,
the close coupling of the data model and its implementation in physical
storage, the consequent high cost of data loading and reorganization.
Another urban myth...